The present invention relates to an anti-Newton ring film, which is composed of a material composed of a polyester film or the like and having good flatness that has been surface treated to avoid interference fringes (Newton rings) generated by objects in contact with each other, and more particularly, to such a film having high transparency.
In the prior art, the problems associated with Newton rings caused by objects in close contact with each other have been found in several applications such as photomechanical process and optical devices. For example, in the photomechanical applications, when separation imaging is performed using a drum scanner for plate making, the Newton rings may be generated by the close contact of a color original matter with a separation drum, causing appearance of the Newton rings in a separation imaged output film. Also, in optical device applications, the Newton rings may be generated by the close contact of a light diffusion plate with a light guide plate in a liquid crystal display, for example, resulting in unevenness in the brightness on the display screen section.
The Newton rings are generated when a spacing (referred to as an xe2x80x9cair layerxe2x80x9d hereinafter) between members in close contact with each other is less than a certain value. Accordingly, the Newton rings can be avoided by keeping the thickness of the air layer larger than the certain value. Many anti-Newton ring films that avoid Newton rings by such a technique have been reported, wherein the film is roughened on one or both side(s) by sandblasting the surfaceorby coating the surface with a liquid agent comprising an inorganic pigment dispersed therein (see, for example, Japanese Patent Application laid open No. H3-144646). These attempts are directed to supporting a contacting member at protrusions on another member (e.g., the film) to keep the spacing (i.e., the air layer) between recesses on the latter member and the contacting member larger than a certain value.
However, in general, materials required to have the anti-Newton ring property are often required to have transparency at the same time. The materials treated according to the above technique can not meet this requirement.
In order to overcome this problem, anti-Newton ring films have been developed and used in which a coating having a rough surface is provided employing a coating liquid comprising a binder and resin particles having excellent transparency dispersed therein (Japanese Patent Application laid open Nos. H5-11429, H9-272183).
These anti-Newton ring films actually have better transparency than the conventional films because the resin particles employed have excellent transparency, but, the coating requires at least 10 weight % of the resin particles based on the binder to provide the anti-Newton ring property. Even resin particles having excellent transparency reduce transparency (total light transmittance) if they are used in an amount greater than 10 weight %. Moreover, a large number of protrusions formed by a large number of resin particles on the coating surface are likely to make scratches on the contacting member during stacking, storage and the like, resulting in deterioration of the optical properties.
On the other hand, if the amount of the resin particles incorporated in the binder of the conventional anti-Newton ring films is reduced (i.e., made less than 10 weight % of the resin particles based on the binder) to improve transparency and xe2x80x9cunscratchingnessxe2x80x9d (the property of making few scratches on a contacting member), the number of the protrusions formed on the coating surface is too small to provide the anti-Newton ring property. That is, since the distance between the adjacent protrusions is increased, the contacting member sags at locations apart from points in contact with the protrusions and the thickness of the air layer cannot be kept larger than a certain value.
The present invention is based on the discovery that the use of an ionizing radiation curable resin as a binder provides the anti-Newton ring property even when a significantly small amount of particulate material is added to the binder to provide an air layer having a thickness which otherwise causes the Newton rings.
In accordance with the present invention, there is provided an anti-Newton ring film comprising a transparent substrate and a resin layer on at least one side of the transparent substrate, wherein the resin layer comprises an ionizing radiation curable resin as a binder and a particulate material dispersed in the binder, at least part of particles constituting the particulate material are protruded from the surface of the resin layer, and the content of the particulate material is in the range between 0.01-0.5 weight % based on the total amount of the binder constituting the resin layer.
The anti-Newton ring film of the present invention has a resin layer formed by incorporating a particulate material into an ionizing radiation curable resin, and has xe2x80x9cundulationxe2x80x9d (wavy protrusions/recesses) over the entire surface of the resin layer, in addition to the protrusions of the particulate material (FIG. 1). The film thus forms a surface shape which provides the anti-Newton ring property even when the air layer has a thickness which otherwise causes the Newton rings. Moreover, since the content of the particulate material is greatly reduced, the anti-Newton ring film has excellent transparency, and makes few scratches on the contacting member because the number of the protrusions of the particulate material is also reduced.
Based on the inventors"" further studies, an anti-Newton ring film which keeps the contact member substantially unscratched is provided by employing a lubricant as the particulate material.
Furthermore, an anti-Newton ring film having outstanding transparency and xe2x80x9cunscratchingnessxe2x80x9d is provided by employing a partially oxidized polyethylene wax as the lubricant.
According to another aspect of the present invention, there is provided a method for imparting an anti-Newton ring property to a light transmissive material by forming a resin layer containing a particulate material dispersed in a binder on the surface of the light transmissive material, wherein a binder containing not less than 25 weight % of an ionizing radiation curable resin is used as the binder and the resin layer is formed so that at least part of particles constituting the particulate material are protruded from the surface of the resin layer.
Preferably, the content of the particulate material is in the range of 0.01-0.5 weight % relative to the binder.